1. Field of the Invention
This invention relates to a method of manufacturing steering wheel, which has a fiber-reinforced synthetic resin rim, a metal center boss and metal spokes.
2. Description of the Related Art
A vehicle is provided with a steering wheel fitted to the upper part of a steering shaft. The driver of the vehicle rotates this steering wheel to activate a steering mechanism which changes the direction of steered wheels, thereby steering the vehicle.
FIG. 31 shows a framework of a conventional steering wheel. A skeleton 2 of carbon steel or aluminum alloy having a center boss 1 at its center, is first manufactured, and the outer part of this skeleton 2 is then covered by a synthetic resin 3 such as for example polyurethane resin, polypropylene resin or soft PVC resin so as to obtain a steering wheel suitable for steering as shown in FIG. 32. The steering wheel is then connected to a steering shaft by a center hole 4 formed in the center of the center boss 1.
To mitigate shocks and protect passengers, an airbag system is provided effectively in the center of the steering wheel. However, when an airbag system is fitted, its weight adds to that of the steering wheel so that the overall weight of the assembly increases.
In this respect, Japanese patent provisional publication No. 59-160666, for example, proposes a steering wheel having a magnesium alloy skeleton which is lighter than aluminum alloy. However this steering wheel was still not sufficiently lightweight. Other Japanese patent provisional publication No. 6206548 proposes a steering wheel wherein prepregs and foam sheets are laminated on a skeleton of low melting point alloy and cured to form a cast, following which the low melting point alloy forming the skeleton was removed by melting. This steering wheel is more lightweight, but it is difficult to manufacture. Further, it is difficult to insert fixing holes in airbag systems, horns and covers.